Secretary of State John Kerry hastily returned Monday to the Middle East in a renewed effort to halt the escalating conflict between Israel and militant group Hamas that has resulted in a sharp increase in civilian deaths over the past few days.

Kerry is going to Cairo, Egypt, where he will join diplomatic efforts to get the sides to accept a November 2012 cease-fire agreement.

A deal offered last week by Egypt to halt nearly two weeks of fighting was rejected last week by Hamas, but accepted by Israeli Prime Minister Benjamin Netanyahu.

At least 430 Palestinians and 20 Israelis have been killed in the fighting.

On Monday, Israeli tank shells struck a hospital in central Gaza, said a health official and a doctor at the facility. The health official said the shells killed at least four people and wounded 60, including 30 medical staff. The Israeli military said it was looking into the report.

President Obama told Netanyahu in a phone call Sunday that the United States continues to support Israel's right to defend itself against Hamas attacks.

But he also “raised serious concern about the growing number of casualties, including increasing Palestinian civilian deaths in Gaza and the loss of Israeli soldiers,” the White House said.

Among those killed in fighting were two Americans -- Max Steinberg, of California, and Nissim Carmeli, of Texas.

They fought for the Israel Defense Forces and were killed in the Gaza Strip, the State Department said Sunday night.

Hamas has rejected the Egypt-brokered deal, supported by Netanyahu, and has turned to governments in Qatar and Turkey for an alternative proposal.

Those countries have ties to the Muslim Brotherhood, which is also linked to Hamas but banned in Egypt.

The conflict started roughly two weeks ago, after three Israeli youths were abducted and killed.

Israelis blamed Hamas-backed Palestinians. And the teens’ deaths were followed almost immediately by what authorities suspect was a retribution attack on a Palestinian youth who was strangled, beaten and burned to death.

The killings were followed by rocket attacks by both sides and Israeli ground forces going into the Gaza Strip.

Kerry says Hamas is also attempting to kidnap Israelis through a network of tunnels that militants have used to stage cross-border raids.

Speaking on “Fox News Sunday,” Kerry declined to answer a question about whether Israeli has gone too far, saying essentially “it's very difficult in these situations.” But he also defended Israel’s effort to take out the tunnels.

United Nations chief Ban Ki-moon is already in the region trying to revive cease-fire efforts.

The U.N. relief agency in Gaza estimates that 70,000 Palestinians have fled their homes amid Israel's military offensive and more than 1,000 homes in Gaza have been destroyed or damaged beyond repair.

Netanyahu said on ABC's "This Week," that Israel has tried to avoid killing Palestinian civilians through phone calls, text messages and leaflets dropped on their communities.

But Hamas doesn't "give a whit about the Palestinians," Netanyahu said. "All they want is more and more civilian deaths."

The prime minister said his top goal is to restore a sustainable peace, but then will ask the international community to consider demilitarizing Gaza to rid Hamas of its rockets and shut down the tunnels leading into Israel. Netanyahu brushed off a question about giving concessions to the Palestinians.

Tensions between Israel and Palestinian authorities have been simmering for years. They threatened to boil over this spring when Israel shelved nearly nine months of peace negotiations that were being personally shepherded by Kerry after Palestinian President Mahmoud Abbas agreed to create a unity government with Hamas.